Pension and Postretirement Benefit Plans and Defined Contribution Plans - Amounts Recognized in Accumulated Other Comprehensive (Loss)/Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans Adjustment [Member]
Defined Benefit Plan Disclosure [Line Items]
Distribution of Upjohn business, before tax		$ 388
Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial losses	[1]	58	$ (76)
Prior service (costs)/credits		688	830
Total	[2]	746	754
Defined benefit plan, derecognition of pre-tax actuarial losses		(50)	38	$ 105
US [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial losses	[1]	(5,062)	(4,812)
Prior service (costs)/credits		(3)	(2)
Total	[2]	(5,065)	(4,814)
Defined benefit plan, derecognition of pre-tax actuarial losses		640	(246)	361
US [Member] | U.S. Supplemental (Non-Qualified) Pension Plans [Member] | Non-Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial losses	[1]	(579)	(484)
Prior service (costs)/credits		(1)	0
Total	[2]	(580)	(485)
Defined benefit plan, derecognition of pre-tax actuarial losses		95	115	(189)
International [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial losses	[1]	(3,056)	(2,921)
Prior service (costs)/credits		(31)	(21)
Total	[2]	(3,087)	(2,942)
Defined benefit plan, derecognition of pre-tax actuarial losses		$ 202	$ 570	$ 84

[1] Primarily represent the impact of changes in discount rates and other assumptions that result in cumulative changes in our PBO, as well as the cumulative difference between the expected return and actual return on plan assets. These accumulated actuarial losses are recognized in Accumulated other comprehensive loss and are amortized into net periodic benefit costs primarily over the average remaining service period for active participants for plans that are not frozen or the average life expectancy of plan participants for frozen plans, primarily using the corridor approach.

[2] The change from December 31, 2019 includes the derecognition of $388 million of pre-tax actuarial losses, net of prior service credits associated with benefit plans distributed as a result of the spin-off and the combination of the Upjohn Business with Mylan on November 16, 2020.